Abstract LB-299: F-dasatinib inhibits glioma cell proliferation and alters expression of PDGFR signaling pathway intermediates in PDGFR-overexpressing glioma models

Abstract

Abstract Current knowledge in tumor biology has enhanced our understanding of the role of kinase receptors, such as platelet-derived growth factor receptor (PDGFR), and associated downstream signal transduction pathways in tumor growth and maintenance. New tyrosine kinase (TK) inhibitors to these receptors and signaling pathways have demonstrated efficacy in certain clinical settings and offer the potential to revolutionize disease treatment. Imatinib mesylate (Gleevec) and PTK787/ZK222684, inhibitors of PDGFR, have failed to show significant clinical benefit as monotherapies. Dasatinib (BMS-354825), a more potent second-generation inhibitor of multiple TK receptors, including PDGFR, has demonstrated promising therapeutic potential in managing intracranial leukemic disease. Here, we assayed the in vitro dose-dependent uptake and inhibitory response of brain tumor cells derived from PDGFR-overexpressing genetically-engineered gliomas, to a novel PDGFR inhibitor and dasatinib analogue (fluorinated dasatinib). In addition, we determined the relative potency of F-dasatinib in vitro, as well as non-invasively assessed PDGFR receptor status and tumor-specific targeting in vivo using radiolabeled dasatinib (18F-dasatinib) and positron emission tomography (PET) imaging. Uptake and inhibitory response of fluorinated dasatinib in vitro was found to be dose-dependent, resulting in cell cycle arrest and alterations in tumor cell proliferation and apoptosis. No difference was seen between BMS-354825 and its fluorinated analogue in terms of tumor cell proliferative or inhibitory responses. Tumor cell proliferation was examined over a range of concentrations (10-200 nM), with significant inhibition seen from 50-150 nM over a 96-h interval; 80% inhibition was found at 150 nM (IC50=10 nM). Serum-starved glioma cells demonstrated total inhibition of cell proliferation in the presence of PDGF (25 ng/ml) and 150 nM F-dasatinib. By contrast, glioma cell proliferation was not significantly inhibited by imatinib or PTK787/ZK222684 over similar concentration ranges. In addition to F-dasatinib being a potent inhibitor of glioma cell proliferation, expression of p-PDGFRalpha and key downstream signaling pathway intermediates were observed; p-ERK, p-Akt and p-Src were inhibited within 15 min of treatment with 150 nM F-dasatinib and in the presence of 10% FBS or 25 ng/ml PDGF. Further, dose-dependent alterations in the percentage of cells in the S phase of the cell cycle (∼100% reductions at 150 nM) and apoptosis were found, the latter effects enhanced up to concentrations of 150 nM and accompanied by increased PARP protein expression at 250 nM F-dasatinib. In vivo studies using GEM glioma models revealed tumor-specific uptake of 18F-dasatinib probe using dynamic PET imaging. These results suggest that, in GEM gliomas, dasatinib analogues may serve as diagnostic or therapeutic biomarkers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-299.